Update: My bichir died after a 50% water change. Perhaps it was too much. I decided not to get another bichir since I was way too attached to the one I had. I went with african cichlids for my new 55 gallon and they are very cool. Can any type of pleco or other bottom feeder go with the african cichlids?
i do 50% water change often and it has never been a problem for my 3 bichirs, as long as you do the water change right, so that you add water with same temperature, ph so on
Tankmates: i find that almoust any type of fish goes well with the bichir as long as it dues fit in its mouth, altho i have had many fish smaller then their mouth that has not been eaten even when they lay by their side (when the bichirs where small pre 1year)
when they got older i gave my small fish to the petstore just because i didnt want to risk them.
later i have had them with freshwater sharks like redtail shark, bala shark, siamese algae eater. and other large fish that dont fit in their mouth, none agressive catfish, snakeheads, oscars, placid cichlids, knifefish, arowana, gars, bowfish, lugfish, larger eel spechies (my bichirs love to hang out with my black ghost knife) and last but not least, other bichirs if they got enough space. (i have 3 different bichirs who goes well together, they use to dogpile and lay on top of each other just chilling)
NOT tankmates: small steaming fish and realy small fish in general, these fish will be snack when your bichirs are older than 1 year.. but as i said. they could work pre 1 year depends on how fed you keep your bichir.
almoust all kinds of plecos are bad when you bichir gets larger and older. the blecos will basicly feed on the bichir like it feeds on drift wood. and it wil suck of the bichir scales and give it infection. and the bichir cant realy do much about it. cus the plecos are extrimely presistent on eating on the bichir.
(i know you dont own bichir anymore, but this is just if someone searching for an answer gets here)